This invention relates in general to systems and accessories used for testing a semiconductor chip package and in particular, to a system for handling and positioning a semiconductor chip package with respect to a testing device for testing the package.
Semiconductor chip packages such as plastic lead chip carriers (PLCC) need to be tested before they are shipped to customers. Typically, the leads of such packages are connected to testing equipment for testing the performance of circuits in the semiconductor chip. For packages having leads which are coplanar, such as quad flat packs or PLCC, the semiconductor chip package is slid down a channel until it is stopped by a stopper. The stopper is positioned such that when it stops the package, the package is adjacent to a testing surface with electrical contacts on the surface for contacting the flat and coplanar side surfaces of end portions of the leads of the package. The package is fed to the channel so that the coplanar side surfaces of the end portions of the leads face the contacts on the testing surface.
When the package is stopped by the stopper so that the package is in adjacent to the contacts on the testing surface, the presence of the package in this position is sensed by a light sensor which supplies a signal to activate a solenoid. The solenoid in turn applies a force to a plunger to move the package towards the testing surface until the substantially coplanar side surfaces of the end portions of the leads of the package are in contact with the contacts on the testing surface. Various signals are then applied to the leads of the package through the contacts in order to test the performance of the circuit in the package.
In order to test the performance of the circuits in a package, the contacts on the testing surface must be in good contact with the side surfaces of the end portions of the leads of the package. For this reason, in conventional semiconductor chip package handling and testing equipment and accessories, the solenoid and the plunger apply a significant force, urging the package towards the testing surface. For this reason, when the side surfaces of the end portions of the leads come into contact with the testing surface, the leads are bent. Typically the solenoid is controlled so that the plunger would push the package until the bottom surface of the package is within a set stand-off from the testing surface for a particular package. In order to ensure that all the leads are in contact with the testing surface, such stand-off is set to a value so that all the leads will be bent when the solenoid stops exerting any force on the plunger. Such fixed value of the stand-off frequently results in excessive bending of the leads which destroys the coplanarity of the end portions of the leads as explained below.
Semiconductor packages are manufactured by manufacturers with certain tolerances. Thus the side surfaces of the end portions of the leads of a package may deviate from the common plane of coplanarity by a certain value within such tolerances when it is sent by the manufacturer. In the subsequent handling of the package, the leads are subject to various forces which may cause the side surfaces of the end portions of the leads to deviate further from the desired common plane. In the conventional chip package handler design, the solenoid is controlled so that the plunger pushes the package towards the testing surface by a fixed distance. For the reasons explained above, the side surfaces of the end portions of the leads of the packages reaching the handler may already deviate from the desired common plane by a significant amount. When such packages are pushed by the plunger by a fixed distance, the existing deviations of the end portions of the leads causes uneven bending of the leads. Such further uneven bending will frequently cause the side surfaces of the end portions of the leads to deviate from the desired common plane by distances greater than that acceptable by the chip user. Such chip packages must either be discarded or the leads reformed in a costly and time-consuming process.
An even greater problem can arise if, within the same batch of packages to be tested, the planes of desired coplanarity of packages in the batch are at different distances from the package body. Thus the plane of desired coplanarity of some packages may be at 25 mils from the package body while those of other packages are at 27 mils. Therefore, if the distance of travel by the plunger is fixed in reference to the packages with planes of coplanarity at 25 mils from the package body, the plunger will cause leads to be severely bent in packages whose planes of coplanarity is at 27 mils to the package body. It is therefore desirable to provide an improved system for handling and positioning the package with respect to the testing surface where such difficulties are avoided.